This invention relates to a method or technique to cure a polymerizable material with various light sources, particularly light curable materials that are selectively cured using special patterns. The patterns are either placed onto a special mask on the materials or onto the curing light tip, or by employing a special light source. As a result from such a segmental curing technique, the polymerization stress associated with the cured materials is limited or minimized due to extended molecular relaxation promoted by this controlled hybrid curing technique.
Light cured materials are well known in the art. For example, it is known in the dental industry to place curable materials into place on a tooth or other dentition to be restored. The materials are then expose to light to effect curing. It has been found that a problem with some such materials is excessive shrinking during the polymerization or cure process.
In the past, many efforts have been made to reduce polymerization shrinkage because it was believed that the lower polymerization shrinkage would always lead to the lower polymerization stress. This is not always correct. For example, rapid polymerization using high powered light indeed resulted in lower polymerization shrinkage for some materials, but was also accompanied by increasing polymerization stresses that could not be relived due to the rapid cross-linked, rigid polymer network developed during fast curing. Recently, it has been understood that it is the polymerization stress that plays a most critical role in determining a successful dental restoration. Therefore, in attempts to reduce stress, various techniques have been explored, including changing the light intensity during curing, changing the spectrum of light distribution, and modulating the curing frequency et al, in addition to new resin development. It should be pointed out that there is one thing in common for all these approaches: one mass of chemically homogenous material is exposed to a relatively homogenous light source resulting in a relatively homogenous curing rate throughout the material.
Light with a defined wavelength can provide proper energy to activate a light curable material and to start polymerization leading a network formation. Such lights used for curing include, for example, visible light and UV light in terms of different frequency or wavelength; there are halogen light, LED light, plasma ARC light, and laser light in terms of different energy. In addition, different light structures, including lamp, filter, light guide have been used in order to change the light output by tuning both spectra and energy distribution. Unless otherwise noted, xe2x80x9clightxe2x80x9d xe2x80x9clight sourcexe2x80x9d and the like refer to any and all such lights, light sources, light guides and the like. Examples of such lights and light sources are discussed by way of example, in U.S. Pat. No. 5,521,392, which is hereby incorporated by reference for such disclosure.
However, with all of these modification, it was noticed that the area exposed directly to such a proper light would always cure first no matter how the light was generated and delivered to the curing surface, which may vary from standard, pulse, ramp to soft-start et al in terms of different curing modes.
It is known that how the materials cure often determines their ultimate performance including polymerization shrinkage, polymerization stress, and their mechanical properties. For restorative dental materials, additional properties like bonding strength, micro-leakage, micro-cracking and post-restoration sensitivity and the like, is believed to be associated with the curing process. Therefore, there has been much effort in the dental industry focussing on the development of new materials and new curing devices.
U.S. Pat. No. 4,385,344 discloses the use a halogen lamp that is filtered to supply light in the range of 400-700 nm. U.S. Pat. No. 5,290,169 discusses a light guide consisting of glass, acrylic, polycarbonate and polystyrene having a head with different concave surface geometry, a tapered section and a curved section to control total light output. U.S. Pat. No. 5,472,991 discloses to generate a light with different wavelengths during two step curing. U.S. Pat. No. 5,634,711 discusses a hand-held LED light with various light energy levels. U.S. Pat. No. 5,879,159 discloses a battery powered hand-held, high power ARC light for fast curing. U.S. Pat. No. 5,912,470 teaches to control total light output in a way to increase light intensity continuously or in stepped form. U.S. Pat. No. 5,975,895 discloses that to generate a series of light pulses at a predetermined frequency, a flash lamp was coupled to the trigger electronics. U.S. Pat. No. 6,008,264 discusses to generate a light with various power, wave form and modulation parameters. U.S. Pat. No. 6,033,223 discloses the use of a laser light and an optical fiber insert to initiate polymerization progressively from a portion thereof adjacent the bottom of the dental cavity towards a surface portion thereof. U.S. Pat. No. 6,079,861 discusses to control total light output from low to very high by two light sources. U.S. Pat. No. 5,229,230 teaches to enhance total incident light intensity on photo-sensitive surface by using new type of photomask with plurality of auxiliary patterns consist of transparent phase shit material spots. U.S. Pat. No. 5,468,577 discloses to increase total light intensity by using new type of photomask with plurality auxiliary patterns of small slots. U.S. Pat. No. 5,835,661 discusses to convert a point-like light into a collimated linear or planar light beam.
This invention relates to a method or technique to cure a polymerizable material with various light sources, particularly light curable materials that are selectively cured using special patterns. The patterns are either placed onto a special mask on the materials or onto the curing light tip, or by employing a special light source. As a result from such a segmental curing technique, the polymerization stress associated with the cured materials is limited or minimized due to extended molecular relaxation promoted by this controlled hybrid curing technique.
With this controlled segmental curing technique, heterogeneous curing zones of polymerization within a chemically homogenous material are created, from which a pre-gel-like behavior is demonstrated during the heterogeneous post-gel stage. The normal polymerization stress generated within those segments initially curing is relieved through stress relaxation within the partially cured or uncured segments adjacent to them. By such segmental stress relief, the severe final stress concentration occurring at the interface between the restorative material and the tooth structure can be avoided. As a result, the associated microleakage and microcracking is limited or minimized. Therefore, this technique can be understood as dividing the stress occurring over the entire composite/tooth interface into a series of incremental stresses over sub-interfaces (composite/composite) that prevents the overall polymerization stress from being transmitted to the composite/tooth interface and/or passed through the interface into the tooth structure. This unique feature is distinguished over other sequential curing techniques, such as soft-start curing, pulse curing, or the like.
An object of this invention is to provide a method by which the polymerizable materials could be selectively cured from the very first surface. As a result of such sectional curing, low polymerization shrinkage and especially low polymerization stress are expected with the cured materials. Because the polymerization stress associated with the cured section could get relief via its adjacent less cured section through normal relaxation.
In general, a method of curing a photo-polymerizable material with light energy from a light source, comprises the steps of exposing at least one selected segment of the material to the light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy.
There is also provided according to the invention, a method of curing wherein said step of exposing a selected segment of the material to light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy includes the steps of fitting the light source with a mask.
Another method, includes such curing wherein the mask has at least one first portion that is substantially transmissive of the spectrum of light required for curing the material.
A further such includes wherein the mask has at least one second portion which is non-transmissive of at least a portion of the spectrum of light required for curing the material.
A still further method includes wherein the second portion of said mask is substantially non-transmissive of the spectrum of light required to cure the material.
Another method includes wherein the steps of exposing at least one selected segment of the material to the light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy, includes interposing a mask between the light source and the material.
An additional method includes wherein said step of selectively limiting exposure of a substantially adjacent segment of the material to the light energy includes preventing at least a portion of the light energy from reaching said adjacent segment.
A further method includes wherein said step of exposing a selected segment of the material to the light energy includes exposing a plurality of selected segments of the material to the light energy.
A still further method includes wherein said step of selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy includes selectively limiting exposure of a plurality of adjacent segments of the material to the light energy.
Another method of curing a photo-polymerizable material comprises the steps of exposing at least one selected segment of the material to light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to said light energy, wherein said step of exposing at least one selected segment of the material to said light energy includes directing light energy from a light source to said selected segment with a light guide comprising a plurality of light-transmitting fiber optic strands and a plurality of light-limiting strands, wherein said light-transmitting strands and said light limiting strands are arranged in a preselected pattern.
Another method of curing a photo-polymerizable material comprises the steps of exposing at least one selected segment of the material to light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to said light energy, wherein said step of exposing at least one selected segment of the material to said light energy includes directing light energy from a plurality of solid state light-emitting devices, such as light emitting diodes, laser diodes or the like, toward the material, wherein said light emitting diodes are arranged in a preselected pattern such that said at least one adjacent segment of the material is not directly exposed to light.
A further method according to the invention for curing a photo-polymerizable material comprises the steps of exposing at least one selected segment of the material to light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to said light energy, wherein said step of exposing at least one selected segment of the material to said light energy includes directing light energy from a plurality of solid state light-emitting devices such as light or laser light emitting diodes, toward the material, wherein at least one of said plurality of light emitting diodes can be selectively controlled to an on state such that it emits light energy, to an off state such that it does not emit light energy.
An additional method of curing a photo-polymerizable material comprises the steps of exposing at least one selected segment of the material to light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to said light energy, wherein said step of exposing at least one selected segment of the material to said light energy includes directing light energy from a plurality of solid state light-emitting devices such as light emitting diodes, laser emitting diodes or the like, toward the material, wherein at least one of said plurality of light emitting diodes emits light of a different wavelength than at least one other of said plurality of light emitting diodes.
A method of reducing polymerization-induced stress in a photo-polymerizable material cured with light energy from a light source, comprises the steps of exposing at least one selected segment of the material to the light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy.
A method of reducing the shrinkage rate of a photo-polymerizable material during curing of the material with light energy from a light source, comprises the steps of exposing at least one selected segment of the material to the light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy.
A method of curing a photo-polymerizable material with light energy from a plurality of light sources, comprises the steps of exposing at least one selected segment of the material to the light energy while selectively limiting exposure of at least one substantially adjacent segment of the material to the light energy, by selectively controlling at least one of the plurality of light sources from an on state wherein light energy is emitted, to an off state wherein light energy is not emitted.
A method of curing a photo-polymerizable material with light energy from a plurality of light sources, comprises the steps of selectively exposing segments of the material to different light energy levels by controlling at least one of the plurality of light sources from an on state wherein light energy is emitted, to an off state wherein light energy is not emitted.
A method of curing a photo-polymerizable material with light energy from a plurality of light sources, comprises the steps of exposing different segments of the material to light energy in a preselected sequence by controlling at least one of the plurality of light sources from an on state wherein light energy is emitted, to an off state wherein light energy is not emitted.
A method of curing a photo-polymerizable material with light energy, comprises the steps of providing at least two light sources, each of said light sources emitting a different wavelength of light, and selectively exposing the material to light from said light sources. A further aspect of this method may be wherein a first segment of said material is first exposed to one of said plurality of light sources, followed by exposure to a second of said plurality of light sources having said different wavelength of light.
A light guide according to the invention for directing light to a photocurable material, comprises a mask to limit the transmission of light to a selected portion of the material.
A mask according to the present invention is interposed between the material to be cured and the light source, for use in curing the photocurable material, and comprises a mask pattern having at least one light limiting block, wherein said mask pattern block substantially prevents at least a portion of the light spectrum required to cure the material from directly reaching the surface of the material to be cured.